1. Field of the Invention
The present invention relates to a wrapper for wrapping bales, in particular bales of crop material wherein each loading arm has a pivotable grip arm mounted, preferably at the distal end thereof, wherein the pivotable grip arms are pivotable with respect to the loading arms between a closed position, in which the distance between the grip arms is smaller than the width of a bale to be wrapped, and an open position in which the distance between the grip arms is larger than the width of the bale, and wherein the at least one actuator is arranged to move at least one of the grip arms between the open and the closed position.
2. Description of the Related Art
Conventional wrappers are known in the art. In a known embodiment of the wrapper, the wrapper comprises a wrapping table mounted on a frame to support the bale during wrapping, and a wrapping device mounted on the frame to wrap wrapping material about the bale. A loading device may be provided to load a bale to be wrapped from a ground surface on the wrapping table.
The loading device is typically a pivotable support structure which can be moved from a pick-up position in which a bale can be picked up from the ground surface to a release position in which the bale can be placed on the wrapping table. The pivotable support structure usually comprises two loading arms between which the bale can be arranged.
Generally, two types of loading devices can be distinguished in the art.
In a first type of loading devices, friction fit is used to lift the bale from the pick-up position to the release position. To load a bale the loading arms are arranged at opposite sides of the bales, and moved towards each other. By the resulting compression force, the bale is held between the two loading arms so that the bale can be lifted from the ground surface. An example of this type of wrapper is the “ELHO Sideliner” manufactured by Elho, Pannainen Finland, also described in Finnish patent publication FI117504, which is hereby incorporated by reference in its entirety.
A drawback of this type of loading device is that the use of forces exerted on the bale to hold the bale by friction may be less reliable, in particular when bales of low compressed crop material are lifted.
In the second type loading device form fitting is used to lift the bale. In such embodiment pivotable grip arms are provided at the distal end of the loading arms, which grip arms can be placed in an open position and a closed position. In the open position, the distance between the grip arms is larger than the width of a bale to be wrapped. In this open position of the grip arms, a bale can be positioned between the two loading arms when the wrapper is driven towards this bale. When a bale is positioned between the loading arms, the grip arms can be moved to the closed position in which the distance between the grip arms is smaller than the width of a bale. As a result, the bale is enclosed by the grip arms, the loading arms and, possibly, further parts of the loading structure. The bale can be lifted by pivotable movement of the loading structure from the pick-up position to the release position, whereby the grip arms support the bale. An example of this type of wrapper is for instance the “Agronic 1020 or 1520” manufactured by Agronic, Haapavesi, Finland, which is hereby incorporated by reference in its entirety.
A drawback of this second type of loading devices is that the movement and actuation of the grip arms requires extra parts. In particular hydraulic cylinders are arranged on the loading arms to move the grip arms between the open position and the closed position. Furthermore, the actuation of the grip arms is carried out in a separate hydraulic circuit, resulting in extra actuation steps by the user of by a control circuit controlling the loading of a bale on the wrapper. In an automatic system extra sensors have to be provided to reliably control the position of the grip arms.
Another drawback of loading devices in general is that the bale has to be relatively accurately positioned with respect to the wrapper before the bale can be successfully loaded on the wrapping table. In known loading devices, the bale to be wrapped is arranged substantially tight-fit between the loading arms to centre the bale with respect to the longitudinal axis of the wrapper. As a consequence, a bale lying on the ground surface has to be accurately approached by the wrapper to precisely position the bale between the loading arms.
As a solution to this drawback, the space between the loading arms could be increased, but this would result in the risk that the bale is positioned off-centre with respect to the longitudinal axis of the wrapper which is undesirable for the wrapping process.